This started off life as a Carawagon 'Continental' I seem to recall, and was owned by Roger (the chap who ran/runs the CASPA forum). It lost its Carawagon fittings a long time ago, and a folding roof was found for sale and fitted in the last few years. Being a Continental, it never had the characteristic folding roof from new. It is a rather early 6 pot indeed, but now sports a mis-match of camper bits from various sources.
Random pop-quiz fact: If I remember correctly, it was once owned by the chap who played cello on many Beatles records, Eleanor Rigby included!
It is far far from being an early or prototype Carawagon. Russell Searle patented the folding roof design in 1961/2 if my memory serves correctly and RJ Searle were an approved LR converter by the time the 1968 price lists were issued (the 1963 price lists only list Martin Walter as approved camper converters). There are a few 'early' Carawagons I have seen, but most seem to be SIIIs. I know of at least two on C plates, both converted from new.